Comodave
Moderator Emeritus
- Joined
- Jul 2, 2015
- Messages
- 22,263
- Location
- Au Gres, MI
- Vessel Name
- Black Dog
- Vessel Make
- Formula 41PC
I believe that I used a 1 amp fuse on my Scad system. So it is really a low draw. And it was simple to install.
Instead of the simple, effective, and inexpensive Uniseal, what about glassing in an elbow and hose barb much like the manufacturer did for the other tank connections? That would be at least as secure a connection and seal, and prevent the protruding pipe thing from reducing the usable tank volume.
Thanks for the info Peggy, this winter I plan on seeing if I can finagle my tank out and redo my vent line to a larger mushroom type. and I will check the discharge pipe also. Plan to replace all the waste lines also. Slowly working down my list but the waste smell is getting closer to the top of the list. If decided to add a second vent line on the opposite side of the boat I should have two fittings into the tank and not just tee off a single fitting?The "protruding" pipe need not extend more than 1/2" inch below the Uniseal.
If your existing tank fittings are in the end of your tank as they are on OEM and off-the-shelf tanks, you're already losing capacity because contents will overflow into the inlet line when the level reaches the bottom of that fitting and a pumpout will leave up to 2" in the bottom of the tank when the level falls to the top of the discharge fitting and begins to suck air. Relocating all the fittings to the top of the tank with a diptube on the discharge fitting that' long enough to touch the bottom of the tank and is cut at about a 25 degree angle (any flatter can trap TP and solid waste under it, any sharper leaves too much in the tank) allows you to use all of the stated (usable) capacity of the tank which is never every last cubic inch..
--Peggie
Very good points. So understanding the impact connections on the side of the tank have on usable volume, a vent tube that protrudes ½ inch below the top of the tank has no impact because that volume was not usable anyway. My connections are well below the top.The "protruding" pipe need not extend more than 1/2" inch below the Uniseal.
I would go with aeration instead of a second vent line (which would need a second thru-hull) 'cuz unless your vent line(s) are relatively short, straight and don't rise more sharply than 45 degrees, a second one wouldn't help much.Thanks for the info Peggy, this winter I plan on seeing if I can finagle my tank out and redo my vent line to a larger mushroom type. and I will check the discharge pipe also. Plan to replace all the waste lines also. Slowly working down my list but the waste smell is getting closer to the top of the list. If decided to add a second vent line on the opposite side of the boat I should have two fittings into the tank and not just tee off a single fitting?
What is your definition of relatively short? I could one side at probably a bit less than 5’ and the opposite side with maybe 7ish’ with a slight uphill definitely might much less than 45 degree.I would go with aeration instead of a second vent line (which would need a second thru-hull) 'cuz unless your vent line(s) are relatively short, straight and don't rise more sharply than 45 degrees, a second one wouldn't help much.
Aeration doesn't have to be expensive...many owners DIY aerators using a bait box pump and some "perforated" (put holes in it) hose. that can deliver air throughout the tank. It does have to run 24-7 whether you're on the boat or not (see my previous posts on this), but the current draw is minimal.
--Peggie
How high above the waterline are they?My boats beam is about 14’. I put a 1.5” one to each side. They go up less than a foot each so it is pretty much a straight shot from side to side.
Thanks, I will be a little more than that. Did you do two vent fittings on the tank?I have not measured it but it is about 1’ 6”.
What is your definition of relatively short? I could one side at probably a bit less than 5’ and the opposite side with maybe 7ish’ with a slight uphill definitely might much less than 45 degree.
Peggy, In my search for answers I found your quote from June 2011. The bolded is what I am interested about. You often say straight, which appears to also mean level or up 45* max and no more than 5 feet.HeadMistress 2011
The vent line has everything to do with creating AEROBIC conditions in the tank.... when it's short enough, straight enough, and of sufficient diameter to allow a free exchange of air with the gasses in the tank.* But the "standard" 5/8" ID vent line can't do that if it's more than about 18" long. A vertical line even that short cannot do that because the gasses in the tank are heavier than air they don't rise, fresh air doesn't fall, so the twain never meet. 5' is about the maximum length that will allow a tank to "breathe."
I have always wondered why not slope downwards but stay above waterline?Carbon dioxide weighs 1.87 kg/m3, so it is 1.5 times the weight of air. Sewage gas is heavier than atmospheric gas and it “sinks” to the lowest level in the house or in a room.
You could, but many tanks aren't mounted high enough in the boat to allow it. The top of my tank is below the waterline, for example.I have always wondered why not slope downwards but stay above waterline?
Ambient air doesn't fall and sewer gasses don't rise...so in a downsloping vent or vents that have bends in them or rises closer to vertical than 45 degrees, or is longer than 6-7', the 'twain will never meet to make any exchange.You could, but many tanks aren't mounted high enough in the boat to allow it. The top of my tank is below the waterline, for example.
That's exactly why I went for forced aeration over adding a second vent and further up-sizing the one vent beyond the 1" hose it currently uses. With the tank mounted so low (and on the centerline) it would be hard to get enough airflow through the vents unless they could be placed such that wind would be regularly forcing air through and out the other side.Ambient air doesn't fall and sewer gasses don't rise...so in a downsloping vent or vents that have bends in them or rises closer to vertical than 45 degrees, or is longer than 6-7', the 'twain will never meet to make any exchange.
--Peggie
Properly functioning vents perhaps, but the vent on MY boat is too long and too twisty to allow sewer gas out or oxygen in. It would be great if it did, but it never has since the boat was built in 2007. That's the understanding I am asking about.am I correct in understanding that my vent is not a gas exchange and oxygen supply mechanism?
Nope...you are incorrect, which is the reason why it's necessary for vent lines to be short enough, straight enough and close enough to horizontal to allow that to happen.